ece475-l15

ece475-l15 - ECE 475/CS 416 Computer Architecture - Wide...

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1 ECE 475/CS 416 Computer Architecture - Wide Issue Processors Edward Suh C omputer S ystems L aboratory [email protected] ECE 475/CS 416 — Computer Architecture, Fall 2007 Prof. Suh Announcements ± Lab 4 is out • Due Nov 30th
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2 ECE 475/CS 416 — Computer Architecture, Fall 2007 Prof. Suh Review ± Tomasulo’s algorithms with ROB • May waste space in RS and ROB • Needs to copy data values many times ± Unified physical register file with register renaming • One register file for both committed and speculative values • More complex to recover from mis-speculation or exceptions ± Handling memory dependence • Load bypassing • Load forwarding ECE 475/CS 416 — Computer Architecture, Fall 2007 Prof. Suh Limit of a Single-Issue Processor ± What is the CPI if all techniques described so far work perfectly? ± Needs to issue more than one instruction per cycle to further improve CPI • ideal CPI becomes width -1 • widely used metric: IPC = CPI -1 ± Two approaches for multiple issue processors: • Superscalar processors – Hazard detection in HW • Very Long Instruction Word (VLIW) processors – Hazard detection in SW (compiler)
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3 ECE 475/CS 416 — Computer Architecture, Fall 2007 Prof. Suh Simple MIPS Superscalar ± Dual-issue superscalar – two datapaths • int/branch/mem (including FP mem) • FP WB fp EX fp EX fp EX fp ID fp IF fp WB int MEM int EX int ID int IF int WB fp EX fp EX fp EX fp ID fp IF fp WB int MEM int EX int ID int IF int WB fp EX fp EX fp EX fp ID fp IF fp WB int MEM int EX int ID int IF int WB fp EX fp EX fp EX fp ID fp IF fp WB int MEM int EX int ID int IF int ECE 475/CS 416 — Computer Architecture, Fall 2007 Prof. Suh Simple MIPS Superscalar ± Dual-issue superscalar • int/branch/mem (including FP mem) • FP (still needs several FPUs) ± IF may have alignment restrictions • hurts at the beginning of a BB • insert NOP in misaligned part during 1 st cycle ± ID may have alignment restrictions • fetched A|B, C|D, E|… may execute as A|-, -|B, C|D if A ± B hazard • but not always as A|-, C|B, E|D, … ± Int/FP partition makes cross-datapath hazards almost trivial
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4 ECE 475/CS 416 — Computer Architecture, Fall 2007
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This note was uploaded on 02/19/2008 for the course ECE 4750 taught by Professor Suh during the Fall '07 term at Cornell.

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ece475-l15 - ECE 475/CS 416 Computer Architecture - Wide...

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